It is known in the prior art to use vehicles as probes for measuring traffic conditions in real-time. Individual vehicles provide “floating car data”, such as, for example, the vehicle's time, speed, position, and heading, which can be used to estimate travel time and traffic speed, and which can in turn be used as an online indicator of road network status, as a basis for detecting incidents, or as input for a dynamic route guidance system.
With reference to FIG. 1 (PRIOR ART), an exemplary prior art probe vehicle system 10 includes a plurality of probe vehicles 12; technology 14 for determining each probe vehicle's location, such as, for example, a system using orbiting satellites, such as the Global Positioning System (GPS), a system using cellular telephones, or a system using radio-frequency identification (RFID); and a wireless communication system 16 for allowing communication between the probe vehicles and a receiving center 18 which receives and processes the data generated by the probe vehicles 12.
There have been few systematic efforts using a general approach to determine the required number of probe vehicles 12 to reliably and adequately measure link-travel time for different road networks. Using traffic simulation methods, different studies have provided widely varying estimates of the number of probe vehicles 12 needed. These studies indicate that, on a freeway, 5% to 7% of the vehicles present must be probe vehicles 12 providing data in order to determine real-time traffic conditions with a sufficiently high level of confidence. In such a scenario, an exceedingly large number of probe vehicles 12 would each communicate frequently with the receiving center 18 in order to provide a relatively small amount of data. An exceedingly large number of communication channels, potentially one for each probe vehicle 12, would be needed to accommodate the frequent data communication. Furthermore, an exceedingly substantial data processing capacity would be needed at the receiving center 18 to process the large volume of incoming data in real-time.